Method and substrates for making photovoltaic cells

ABSTRACT

Methods of and apparatuses for making a photovoltaic cell are provided. The photovoltaic cell is able to have a substrate made of a composite material. The composite material is able to be formed by mixing a binder and a physical property enhancing material to form a mixer. The binder is able to be pitch, such as mesophase pitch. The physical property enhancing material is able to be fiber glass. The substrate of the photovoltaic cell is able to be flexible, such that the photovoltaic cell is able to be applied on various surfaces.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Patent Application is a divisional of U.S. patent application Ser.No. 13/274,223, filed Oct. 14, 2011, titled, “METHOD AND SUBSTRATES FORMAKING PHOTOVOLTAIC CELLS,” now U.S. Pat. No. 9,184,323 which claimspriority from U.S. Provisional Patent Application Ser. No. 61/455,060,filed Oct. 15, 2010 and entitled “NOVEL SUBSTRATES FOR MATERIALSAPPLICATION,” and U.S. Provisional Patent Application Ser. No.61/455,061, filed Oct. 15, 2010 and entitled “NOVEL SUBSTRATES FOR PHOTOVOLTAIC APPLICATIONS,” which are all hereby incorporated herein byreference in their entirety for all purposes.

FIELD OF THE INVENTION

The present invention relates to the field of green technology. Morespecifically, the present invention relates to the field of photovoltaiccells.

BACKGROUND OF THE INVENTION

Traditionally, sodalime glass is used for the fabrication of thin filmsolar cells. Problems are associated with the photovoltaic cells thatuse sodalime glass or stainless steel sheets as substrates. The sodalimeglass substrates are brittle. Furthermore, the sodalime glass substrateis rigid and not flexible, which limits its applications to only flatsurfaces. Moreover, the sodalime glass substrate is an electricalinsulator and is expensive, which is about 40% of PV fabrication cost.The high cost of the substrate material results in a high price of thefinished devices. Additionally, the Tg (glass transition temperature) ofsodalime glass substrate limits the selenization temperature. Comparingthe more recent PV cell with a stainless steel sheet or a metallic sheetas a substrate with the traditional PV cell with sodalime glass as asubstrate, the stainless steel/metallic sheet substrate has a moreflexible and conductive structure than the sodalime glass substrate. Theflexibility increases the uses of the PV cell. Nonetheless, the rolledstainless steel sheet substrate is inferior than the sodalime glasssubstrate in a way that the stainless steel substrate has a roughersurface. Moreover, the metal contained in the typical stainless steelsubstrate is able to be a source of metallic contamination (such as Fe,Ni, and other impurities) to CIGS semiconductors, because the metalscontained (such as Fe and Ni) is able to diffuse through Mo grainboundaries to short the cell. Especially, the typical selenizationtemperature under inert atmosphere is between 500° C. and 750° C. Atsuch temperature, the diffusion rate of Fe and Ni becomes very fast andthe kinetics favors Fe diffusion through the open grain boundary betweenMo grains. Also, at this high temperature, molten Se in the CIS (copperindium selenide) or CIGS (Copper indium gallium (di)selenide: atetrahedrally bonded semiconductor) layer above the Mo diffuses throughthe Mo grain boundaries to attack the stainless substrate beneath theMo, shorting out the solar cells. These defects typically result incells with greatly reduced efficiencies and the substrates are oftenscrapped. High scrap loses and accompanying low efficiency cellsproduces expensive solar cells, which are not commercially viable.

SUMMARY OF THE INVENTION

A method of and a novel substrate for making a photovoltaic cell isprovided. The photovoltaic cell is able to have a substrate made of acomposite material. The composite is able to be formed by mixing abinder and a physical property enhancing material to form a mixer. Thebinder is able to be pitch, such as mesophase pitch or neomesophasepitch. The physical property enhancing material is able to be aconducting material, a nonconducting material, or fiber glass. Thesubstrate of the photovoltaic cell is able to be flexible or rigid, suchthat the photovoltaic cell is able to be applied on various surfaces.

In the first aspect, a photovoltaic cell comprises an absorber capableof absorbing light and a substrate, wherein the substrate comprises acarbon based material, a silicon based material, or a combinationthereof, wherein the carbon based material, the silicon based material,or the combination thereof is substantially free of metal. In someembodiments, the carbon based material, the silicon based material, orthe combination thereof comprises a pitch. In other embodiments, thepitch comprises mesophase pitch, neomesophase pitch, oriented carbonstructures or a combination thereof. In some other embodiments, theabsorber comprises CIGS, CIG, or CIS. In some embodiments, thephotovoltaic cell further comprises CdS, Mo, Cr, or a combinationthereof. In other embodiments, the substrate comprises fiber glass. Insome other embodiments, the substrate comprises a conductive material.In some embodiments, the substrate comprises an insulator. In otherembodiments, the substrate is flexible. In other embodiments, thesubstrate is rigid.

In the second aspect, a method of manufacturing a photovoltaic cellcomprises preparing a substrate containing a carbon based material, asilicon based material, an orientated carbon structure or a combinationthereof, wherein the carbon based material, the silicon based material,or the combination thereof is substantially free of metal and coupling alight absorber with the substrate. In some embodiments, the carbon basedmaterial, the silicon based material, or the combination thereofcomprises pitch. In other embodiments, the method further comprisescoating an adhesive layer between the light absorber and the substrate.In some other embodiments, the adhesive layer comprises Cr. In someembodiments, the method further comprises forming a reflective layerbetween the adhesive layer and the light absorber. In other embodiments,the reflective layer comprises Mo. In some embodiments, the lightabsorber comprises CIGS, CIS, or CIG. In other embodiments, the methodfurther comprises performing selenization. In some other embodiments,the pitch comprises mesophase pitch. In some embodiments, the substratecomprises a silicon/silicone based material or a carbon based material,such as fiber glass and ceramic compounds.

In the third aspect, a method of manufacturing a photovoltaic cellcomprises forming a mesophase or neomesophase pitch by performing asolvent extraction, a heat treatment, or a combination thereof, dryingthe mesophase or neomesophase pitch, adding a filler material, extrudingsheet of composite material, and stabilizing or cross-linking the pitchat a temperature above 200° C., such that a substrate of thephotovoltaic cell is formed. In some embodiments, the method furthercomprises performing extrusion of the mesophase or neomesophase pitch insheet form above 200° C. In some embodiments, the sheet structure issimilar to a plywood structure. In other embodiments, the method furthercomprises performing a high temperature treatment at a temperaturebetween 600° C. and 3000° C. In some other embodiments, the fillermaterial comprises fiber glass. In some embodiments, the filler materialcomprises a conductor. In other embodiments, the filler materialcomprises an insulator. In some other embodiments, the method furthercomprises coupling a light absorber with the substrate. In someembodiments, the light absorber comprises CIGS, CIS, or CIG.

In the fourth aspect, a method of forming an insulating apparatuscomprises preparing a composite material containing pitch with fiberglass and coupling the composite material with a building structure,wherein the substrate is able to reflect heat, lights, or a combinationthereof. In some embodiments, the composite material is able to reflectmore than 90% of incoming light, such as IR (infrared radiation) and UV(ultraviolet) light. In some embodiments, the composite material is ableto reduce heat from entering into the building structure. In someembodiments, the composite material is able to conduct electricity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a method of making a material in accordance with someembodiments.

FIGS. 2A and 2B illustrate apparatuses for making a substrate materialin accordance with some embodiments.

FIG. 3 illustrates a photovoltaic cell in accordance with someembodiments.

FIG. 4 illustrates a photovoltaic cell manufacturing method inaccordance with some embodiments.

FIG. 5 illustrates a mesophase pitch sheet fabrication method inaccordance with some embodiments.

FIG. 6 illustrates a mesophase pitch sheet fabrication method inaccordance with some embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In some aspects of the present invention, inexpensive and/or recycledindustrial waste are used to make various materials. The materials havewide applications in industries. For example, the material is able to beused as part of the substrate of a photovoltaic cell. The industrialwastes that are used herein include pitch from the petrochemicalindustry and coal ash from the coal industry and coal fired electricgenerating plants. The above-mentioned waste products (such as pitch andcoal ash) are able to be used as a substrate material for flexible andnon-flexible thin film photovoltaic cells. Above listed industrialwastes are examples that are used for illustration purposes. Otherindustrial waste products are applicable.

In some other aspects of the present invention, materials and compositestructures are formed using isotropic, anisotropic mesophase pitch,graphitizing pitch or liquid crystalline obtained from pitch (includingcommercially available pitch) as a binder or matrix material with othercarbonaceous and or non-carbonaceous materials.

In the following, methods of and apparatuses for making materials aredisclosed in accordance with some embodiments. FIG. 1 illustrates amethod 100 of making the materials in accordance with some embodiments.The method 100 is able to include adding desired/pre-selected materials,creating a laminate with the added materials, stabilizing and/orcross-linking a binder material, and carbonizing. The steps of method100 are optional. Additional steps are able to be added to the method100. The sequences of performing the steps of method 100 are able to bein any order. More details of performing method 100 are illustratedbelow. The method 100 is able to begin from Step 102.

At Step 104, selected materials/components are added based on a selectedmaterial property of the material. In some embodiments, woven fiberglassmaterial (silica-based and/or carbon-based material) is impregnated witha binder material by spraying, roll-coating, dipping, brushing, or acombination thereof. The fiberglass material combined with the bindermaterial forms a binder material coated fiberglass material. A person ofordinary skill in the art appreciates that other methods are able to beused to combine the binder material and the added material to gainpredetermined physical interactions and properties, such as mixing,blending, and pressing. In other embodiments, non-woven fiber glassmaterial is used to be combined with the binder material. The bindermaterial described herein is able to be pitches, coal ash, or any othermaterials that are able to be used as a binder material. A person ofordinary skill in the art appreciates that the binder material is ableto be any materials that have property of adhesion, such as adhesives,glues, cement, and paints. The property of adhesion includes materialsthat show such property under pre-defined conditions, such astemperature, pressure, solvent, co-reactants, or a combination thereof.For example, a binder material is within the scope of the presentinvention when the binder material demonstrates the property of adhesionunder a pressure, such as 10 psi, and not adhesive under normalatmospheric pressure (e.g., 1 atm). Various other components are able tobe added at Step 104 based on the pre-selected property of the products.Some of the embodiments are discussed in the following paragraphs.

At Step 106, a laminate including the added material is created. In someembodiments, the above formed binder material coated fiberglass materialis rolled or extruded to form a laminate. In some embodiments, thethickness of the laminate is thinner than 20 microns. In some otherembodiments, the thickness of the laminate is thicker than 2000 microns.In some other embodiments, the thickness of the laminate is between 20microns and 2000 microns. In some embodiments, the width of the laminateis in the range between 10 cm and 1 m, such that a sheet of a laminatematerial is able to be made for further cutting. In some otherembodiments, the width of the laminate is in the range between 0.5 cmand 3 cm, such that a cell/rectangular form of a substrate is formed forready-to-use. A person of ordinary skill in the art would appreciatethat any width of the laminate is applicable depending on a selected useof the substrate.

In some embodiments, the laminate includes a structure having amesophase pitch layer sandwiched by layers of fiber glass on the topside and on the bottom side of the mesophase pitch layer. For example, asandwich structure/laminate is formed by preparing a first layer offiber glass sheet having a size of 1 m² and a thickness of 3 mm, addinga second layer of a binder material (such as a mesophase pitch) having asize of 1 m² and a thickness of 5 mm on top of the first layer, adding athird layer of fiber glass sheet having a size of 1 m² and a thicknessof 2 mm, and extruding with a pressure press extruder to form asandwiched laminate having a thickness of 7 mm. In other embodiments,the laminate includes a layer of fiber glass sandwiched by two layers ofpitch. In some embodiments, the pitch is a low molecular weightneomesophase pitch or is any other binder.

At Step 108, the binder material is stabilized or cross-linked below thesoftening temperature in an oxygen ambient to form a treated material.In some embodiments, the temperature is in the range of 200° C. to 450°C. A person of ordinary skill in the art appreciates that othertemperature ranges are applicable. In some embodiments, the temperatureis near the softening temperature. In some other embodiments, thetemperature is higher than the softening temperature.

At Step 110, the treated material is heat treated to carbonize themixture. In some embodiments, the temperature of Step 110 is in therange of 800° C. to 1700° C. In some other embodiments, the temperatureis in the range of 700° C. to 3000° C. In some embodiments, the Step 110is performed under inert ambient, such as nitrogen, with a pressurebetween 2 psi and 40 psi. In some embodiments, the pressure applied ismaintained during the cooling down step, such that shrinkage and warpageof the sheet structure is able to be minimized. The method 100 is ableto stop at Step 112.

Different material properties are selected for different applications,such as thermal, sound, electrical, vibrational, signal, and lightconductivity/insulation, material strength, and material durability.Various materials are able to be added in the composite material toenhance the pre-determined property. In some embodiments, chopped orparticulate conducting materials are used as the reinforcing agent ormaterial, such that the conductivity of the material produced is able tobe enhanced. In some other embodiments, chopped or particulatenon-conducting materials are used as the reinforcing agent or material,such that the property of insulation of the material produced isenhanced. In some embodiments, the materials that are incorporatedinclude coal ash, milled glass, milled quartz, glass beads, choppedglass fiber, chopped quartz fiber mica flakes, ceramicpowder/beads/flakes, and non-carbonaceous material. In some otherembodiments, the materials that are incorporated include conductingmetallic or metal alloy powders, flakes or fibers. In some embodiments,the materials that are incorporated include nanoparticles, such as metalnanoparticles and metal oxide nanoparticles (e.g., Cr₂O₃ nanoparticlesare incorporated as a catalyst for neucleation.) A person of ordinaryskill in the art appreciates that any conducting materials are able tobe added including copper, chromium, carbon powder or carbon flakes,graphite flakes, or combinations thereof.

In some embodiments, the electrical resistivity of the substratematerial (the material produced from the method 100) is selected. Insome embodiments, an amount of less than 5% of sulfur or organo-sulfurcompounds with or without metallic oxides or metallic compounds isadmixed into the mesophase pitch binder before the cross-linking stepsuch that glassy carbon is formed during the high temperaturecarbonization step. Any other materials that are able to be added to,for example, control the texture or strength and increase or decreasethe resistivity of the substrate materials are within the scope of thepresent invention.

In the following, the apparatuses for making the substrate material aredisclosed. FIGS. 2A and 2B illustrate apparatuses 200 and 211 for makingthe substrate material in accordance with some embodiments. Thereactants, such as the fiber glass 216 and binder materials 218, areable to be added in the mixing device 202 through the hopper 210 and212, respectively. The reactants are able to be in solid and/or liquidform of solvent and/or compositions. In some embodiments, the mixingdevice 202 is able to be an extruder. The mixing device 202 is able tomix the materials added by the mixer 217, such as a screw mixer. Aperson of ordinary skill in the art appreciates that any number ofhoppers are able to be included in the mixing device 202. The mixingdevice 202 and/or the apparatus 200 are able to be performed under airatmosphere, inter atmosphere (such as N₂ and Ar), or pressurizedatmosphere (such as 2-10 psi and 1-3 atm). The hoppers 210 and 212 areable to be hermetically sealed chambers, top open chambers, hinged topopening chambers for solid and fluids, such as gas, liquid, andsupercritical fluids. The mixing device 202 is able to include a die 214allowing the output material 201 to be shaped in a desired form andthickness, such as 1 mm-10 mm. In some embodiments, the apparatus 200 isable to include a roller 204, such as a pull roller. The roller 204 isable to use its rolling wheels and belts compressing the output material201 to a desired thickness, such as 20 to 500 microns. The laminatedescribed in FIG. 1 is able to be fabricated in a batch mode orroll-to-roll depending on the thickness of the laminate using the mixingdevice 202 and/or the roller 204 described herein. The output material201 is able to be heated in the oven 206 in a pre-determinedtemperature, such as 200° C.-450° C. for stabilizing or cross-linkingthe binder material and 600° C.-1700° C. for carbonizing the materials.In some embodiments, during the stabilization and carbonization steps, acontrolled fluid ambient is used to exact the pressure on both majorsides of the substrate. For example, the oven/furnace 206 is able to belined with tiny orifices 205 (with multiple heating zones), where thegap between the upper and the lower inner furnace walls is negligiblecompared to the width or length of the furnace. In some embodiments,inert gas is introduced into the oven/furnace 206 in the carbonizingprocess through the tiny orifices 205 on both side of the laminate inthe oven/furnace 206 and the pressure of the fluid is controlled toemanate on both sides of the laminate (output material 201), such thatthe fluid, such as inert gas, prevents the sheet laminate from touchingthe major sides of the oven/furnace 206. In some embodiments, the gap ofthe fluid exit 203 of the oven 206 is reduced, such that the appliedfluid is able to be used to exact the pressure on the substrate duringthe cross-linking, carbonization, or a combination thereof. In someembodiments, the apparatus 200 is able to include one or more coolingdevice 207. The output material 201 is able to be cut and stored by acutter 208 to a pre-determined dimension, such as 1 m². The cutter 208is able to be a pressure press-cut machine.

Similar to the protrusion setup device 202, FIG. 2B shows a pultrusiondevice 220. The pultrusion device 220 is able to continuouslymanufacture composite materials. A fiber sheet 226 is able to be pulledthrough the pitch bath 224, which is supplied by a pitch source 222. Theoutput material 201 in FIG. 2B is able to be further compressed by theroller 204, heated by the over 206, cooling down by the cooler 207, andsized by the cutter 208 similar to the processes described in FIG. 2Aand its associated texts.

Applications

The materials that are made by using the methods and apparatusesdisclosed herein in accordance with some embodiments are able to beapplied in various applications and used in various ways. For example,in some embodiments, more than one laminate is able to be stacked andbonded by a thin layer of mesophase pitch binder. The orientation of thesheets is able to be parallel to each another, cross-ply, or in anyselected orientations with respect to each other prior to thecross-linking step. The single sheet or stacked sheets are able to becut and formed in a suitable mold by known methods for fabricating apre-selected structure or shape, such as a substrate of a solar cell.

In some embodiments, an alternatively conductive layer structure isselected, which is able to be made by bonding the highly conductivelaminates to each other by using the more insulative glassy carbonbinder. The formed material having alternative layers of differentconductivity is able to be used as a capacitor for low or hightemperature applications. For example, the capacitor is able to have astructure including a first layer of highly insulating layer, a secondlayer of conducting layer, a third layer of highly insulating layer, afourth layer of conducting layer, and a fifth layer of highly insulatinglayer. The substrate made through the methods and apparatuses disclosedherein is able to be used as flexible substrate for photovoltaic cells,electromagnetic shielding, casing for electronic appliances andarchitectural applications.

Photo Voltaic Cells

In the following, methods of making photovoltaic cells (PV) using thematerial/substrate made above are provided in accordance withembodiments.

Methods of and substances for making photovoltaic cells in accordancewith some embodiments are disclosed. In some embodiments, thephotovoltaic cells include a composite or a non-composite carbonaceoussubstrate, in which isotopic or anisotropic mesophase pitch,neomesophase pitch, or a combination thereof is used as a binder, matrixmaterial, or the neat material for the fabrication of planar and nonplanar sheets for the fabrication of thin film solar cells. In thefollowing, a photovoltaic cell having a substrate using the materialdisclosed herein is provided in accordance with some embodiments.

FIG. 3 illustrates a photovoltaic cell 300 in accordance with someembodiments. In some embodiments, the photovoltaic cell 300 includes asubstrate 302, an adhesive layer 304, a Mo layer 306, an absorber layer308, a buffer layer 310 (such as a CdS layer), and TCO (transparentconduction oxide) layer 312. The substrate 302 of the photovoltaic cell300 is able to include a mesophase/neomesophase pitch backbonesubstrate. In some embodiments, the thickness of the substrate 302 isable to be 20 microns to 1 mm or more. In some other embodiments, thethickness of the substrate 302 is able to be thicker than 5 mm. A personof ordinary skill in the art appreciates that any thickness of thesubstrate 302 is applicable. The physical and material properties of thesubstrate 302 is adjustable by adding pre-selected fillers based on theapplications. The rigidity/flexibility, conductivity, the degree ofthermal expansion, and surface roughness for the substrate 302 are alladjustable and controllable. For example, a conductive substrate 302 isable to be made by adding conductive materials, catalysts,nanoparticles, and metallic oxides (e.g., a filler) to the bindermaterial during the manufacturing process. When an insulating substrate302 is desired, the insulating substrate is able to be made by addinginsulating materials to the binder material during the manufacturingprocess. Similarly, a flexible substrate 302 is able to be made byadjusting the hardness or stiffness of the binder materials or the typesof materials to be added. The substrate 302 made using the methods andmaterials disclosed herein is able to withstand a higher selenizationtemperature range than the substrate made by typical methods. Since thesubstrate 302 made using the methods and materials disclosed herein hasminimal to no undesirable metallic impurities, short of the cell is ableto be avoided when heating the photovoltaic cell under a hightemperature.

In some embodiments, the photovoltaic cell 300 includes an adhesivelayer 304. The adhesive layer 304 is able to be a Cr layer and appliedon top of the substrate 302 by sputtering and other known methods. Thethickness of the adhesive layer 304 is able be between 20 nm to 1000 nm.A person of ordinary skill in the art appreciates that any thickness ofthe adhesive layer 304 is applicable, such as 2 mm or thicker.

In some embodiments, the photovoltaic cell 300 includes a Mo layer 306.The Mo layer 306 is able to be on top of the adhesive layer 304. The Molayer 306 is able to serve as the back contact and to reflect mostunabsorbed light back into the absorber layer 308 (such as a CIGSlayer). The Mo layer 306 is able to be a thin film deposited by PVD(physical vapor deposition) such as sputtering and evaporation and otherknown methods, such as CVD (chemical vapor deposition). The thickness ofthe Mo layer 306 is able to be between 100 nm to 2000 nm. A person ofordinary skill in the art appreciates that any thickness of the Mo layer306 is applicable, such as 2 microns or thicker. In some embodiments,multiple Mo layers 306 are able to be included to attain a pre-definedMo film thickness. In some embodiments, a thin layer Mo alloy (such as a2 nm to 10 nm MoSi layer) is inserted within the Mo laminate to modifythe grain structure of the Mo film coated over the alloy layer.

In some embodiments, the photovoltaic cell 300 includes an absorberlayer 308, such as CIGS layer or a CIG/CIS layer. The absorber layer 308is able to be formed by depositing/sputtering/evaporating precursormaterials/layers, such as Cu, In, Ga, or a combination thereof on the Molayer 306 followed by selenization. The absorber is able to be formedusing typical methods of forming CIGS layers. In some embodiments, theprecursor materials/layers are able to be coated with a thin layer ofsodium fluoride prior to the selenization step in inert ambient betweenthe temperature of 500° C. and 800° C. for 5 minutes to 120 minutes inexcess selenium ambient, such as H₂Se or Se_((g)).

In some embodiments, the photovoltaic cell 300 includes a buffer layer310. The buffer layer 310 is able to be n-type CdS. The buffer layer isable to be coated on the absorber layer 308 by typical methods. In someembodiments, the photovoltaic cell 300 includes a transparent conductingoxide layer (TCO) 312. The TCO layer 312 is able to be doped with Al.The TCO layer is able to collect and move electrons out of the cellwhile absorbing as little light as possible. In some embodiments, thephotovoltaic cell 300 includes electrical wiring elements 314 on the TCOlayer 312 for conducting electronic signals and electricity. In someembodiments, the photovoltaic cell 300 is able to be laminated withpolymer films to form flexible solar cells.

FIG. 4 illustrates a photovoltaic cell manufacturing method 400 inaccordance with some embodiments. The method 400 is able to begin fromStep 402. At Step 404, an adhesive layer is coated on a substrate. Thesubstrate is able to be manufactured using the method described above.In some embodiments, the adhesive layer contains Cr or a Cr sheet/layer.In some embodiments, the substrate is a mesophase matrix substrate. Themesophase matrix substrate is able to be a bottom electrode of thephotovoltaic cell. In some other embodiments, the substrate is acomposite carbonaceous substrate. In other embodiments, the substrate isa non-composite carbonaceous substrate. The substrate is able to beisotropic or anisotropic mesophase pitch, neomesophase pitch, or acombination thereof. A person of ordinary skill in the art appreciatesthat other materials that are adhesive or adhesive under predeterminedconditions are applicable. At Step 406, a Mo layer is coated on theadhesive layer, which is able to couple the substrate with an absorberlayer. At Step 408, precursor materials, such as Cu, In, Ga, and Se(Copper indium gallium selenide), are coated on the Mo layer. At Step410, selenization is performed. In the process of selenization, Se isable to be supplied in the gas phase (for example as H₂Se or elementalSe) at high temperatures, and the Se becomes incorporated into the filmby absorption and subsequent diffusion. By performing the selenization,an absorber of the photovoltaic cell is able to be formed. At Step 412,CdS layer formation on the absorber (CIGS) layer is performed. At Step414, a layer of TCO is coated on the CdS layer. At Step 416, wiringelements are fabricated on the TCO. The method 400 is able to stop atStep 418. In the following, a method of forming the mesophase pitchsheet that is able to be used as the substrate in the method 400described above is provided.

FIG. 5 illustrates a mesophase pitch sheet fabrication method 500 inaccordance with some embodiments. The method 500 begins from Step 502.At Step 504, a pitch is added. The pitch is able to be graphitizableisotropic carbonaceous pitch from Ashland 240 or 260 (petroleum pitch)from coal. A person of ordinary skill in the art appreciates that thepitch is able to be from various sources, such as directly fromindustrial waste. At Step 506, solvent extraction and heat treatment isperformed with the pitch. At Step 508, mesophase or neomesophasematerials are formed. In some embodiments, the mesophase or neomesophasematerials contain liquid crystals more than 50% of the composition. AtStep 510, the mesophase or neomesophase materials are dried andcommunition is performed. At Step 512, sheet extrusion is performedunder inter ambient atmosphere at 250° C. to 300° C. At Step 514, sheetstabilization is perform by heating the sheet at 250° C. to 300° C. AtStep 516, high temperature treatment is performed at inert ambient at600° C. to 3000° C. The method 500 is able to stop at Step 518. In thefollowing, a method of incorporating filler materials into the substratematerial/mesophase sheet material is provided.

FIG. 6 illustrates a mesophase pitch sheet fabrication method 600 inaccordance with some embodiments. The method 600 begins from Step 602.At Step 604, a pitch is added. The pitch is able to be graphitizableisotropic carbonaceous pitch from Ashland 240 or 260 (petroleum pitch)from coal. A person of ordinary skill in the art appreciates that thepitch is able to be from various sources, such as directly fromindustrial waste. At Step 606, solvent extraction and heat treatment isperformed. At Step 608, mesophase or neomesophase materials are formed.In some embodiments, the mesophase or neomesophase materials containliquid crystals more than 50% of the composition. At Step 610, themesophase or neomesophase materials are dried and communition isperformed. At Step 611, filler material is added. The filler to be addedis able to be chosen based on the pre-selected physical/chemicalproperty of the substrate (product). At Step 612, sheet extrusion isperformed under inter ambient atmosphere at 250° C. to 300° C. At Step614, sheet stabilization is performed by heating the sheet at 250° C. to300° C. At Step 616, low melting point and/or low molecular weightmesophase pitch is formed, which is able to be used to laminate multiplesheet material. The method 600 is able to stop at Step 618.

All steps described above are optional. The sequence of performing thesteps that are included in the methods above is able to be in any order.Additional steps are able to be added.

The present application is able to be utilized in making variousmaterials for industrial applications, such as the substrate of a solarcell. In operation, a photovoltaic solar cell with a flexible substratemade with the methods provided herein is able to be bent to a desiredshape and applies on a non-flat surface.

The term pitch used herein is able to include tar, asphaltene,viscoelastic polymers, asphalt, bitumen, carbon disulfide, and resin. Insome embodiments, the high viscosity of the chosen binder (such aspitch) or the added material provides a function to retain the metallicparticles in the substrate and prevent them from shorting the PV cell.In some embodiments, the materials/substrates made using the methods andcompositions disclosed herein is able to be used as a heat insulationdevice, like thermal paint, which is able to be installed on/apply on oras a part of the roof or wall of a building structure, such as a houseor a barn. In some embodiments, the materials/substrates compriseconductive material having high electrical conductivity, so thematerials/substrates are able to be used to conduct electricity. In someother embodiments, the materials/substrates have high reflectivity ofheat and/or lights, and the substrates and the materials are able to beused as mirrors on building structures. The mirrors described herein areable to reflect/insulate/isolate heat, lights, or a combination thereof.In some embodiments, the substrates/materials are able to reflect morethan 90% of the incoming lights or selected wavelengths of lights, suchas IR and UV.

The present invention has been described in terms of specificembodiments incorporating details to facilitate the understanding ofprinciples of construction and operation of the invention. Suchreference herein to specific embodiments and details thereof is notintended to limit the scope of the claims appended hereto. It will bereadily apparent to one skilled in the art that other variousmodifications may be made in the embodiment chosen for illustrationwithout departing from the spirit and scope of the invention as definedby the claims.

What is claimed is:
 1. A method of manufacturing a photovoltaic cellsubstrate comprising: a. forming a mesophase or neomesophase pitch byperforming a solvent extraction, a heat treatment, or a combinationthereof; b. drying the mesophase or neomesophase pitch; c. adding afiller material; d. stabilizing or cross-linking the pitch at atemperature above 200° C., such that a substrate of the photovoltaiccell is formed; and e. carbonizing the pitch under a high temperatureand forming glassy carbon by adding an amount of less than 5% of sulfuror organo-sulfur compounds.
 2. The method of claim 1, further comprisingperforming extrusion of the mesophase or neomesophase pitch above 200°C.
 3. The method of claim 1, further comprising performing a hightemperature treatment at a temperature between 600° C. and 3000° C. 4.The method of claim 1, wherein the filler material comprises fiberglass.
 5. The method of claim 1, wherein the filler material comprises aconductor.
 6. The method of claim 1, wherein the filler materialcomprises an insulator.
 7. The method of claim 1, further comprisingcoupling a light absorber with the substrate.
 8. The method of claim 7,wherein the light absorber comprises CIGS, CIS, or CIG.
 9. A method offorming an insulating apparatus comprising a. preparing a compositematerial containing pitch with fiber glass; b. carbonizing the pitchunder a high temperature and forming glassy carbon, by adding an amountof less than 5% of sulfur or organo-sulfur compounds; and c. couplingthe composite material with a building structure, wherein a pitch basedsubstrate, including the composite material, is able to reflect heat,lights, or a combination thereof.
 10. The method of claim 9, wherein thecomposite material is able to reflect more than 90% of incoming light.11. The method of claim 9, wherein the incoming light comprises IR. 12.The method of claim 9, wherein the composite material is able to reduceheat from entering into the building structure.
 13. The method of claim9, wherein the composite material is able to conduct electricity.